Improved comments.

Explained an important behauvior of firstPath which is relevant for flow
algorithms.
Added a function
Fixed erwigs maxflow for empty graphs.
Bugfixing
Added some shorthands.

Added shorthands for random graph generation to avoid duplicating them
in
every file using those.
Improved comments and removed useless type class constraints from FlowNetwork.
Minor changes.
Overall refactoring.
Increased version to reflect increased code quality.